This invention relates to a system and method for determining the geolocation of a transmitting mobile unit, and more particularly, this invention relates to a system and method of determining the geolocation of a mobile unit using a hybrid GPS system.
As wireless phones and the use of other mobile communication units have become commonplace, the need to locate the users of such devices when in distress or for tracking purposes has grown. For example, it may be necessary to determine the location of a mobile unit, such as a caller on a cellular phone in an automobile, when an emergency occurs. There exists a ruling that will soon require that any mobile 911 caller be located within 125 meters of their location based on the call. Additionally, the need to locate automobiles, construction equipment or other objects for purposes of theft recovery or utilization optimization has also grown. Some telecommunications companies are now building wireless telephones that have a global positioning system (GPS) unit inserted into the handset. The location of the phone is determined by the GPS unit and may be reported over the phone. However, there will often be times when a global positioning system unit does not operate correctly, such as in dense urban areas. For example, it is well known that reception of a GPS signal from satellites by a mobile receiver is often blocked by buildings, particularly in dense urban areas.
There are some non-GPS based systems where the location of a mobile unit can be determined from parameters, such as signal strength, angle-of-arrival (AOA), time-of-arrival (TOA), multipath profile or other characteristics of the signal. An example is disclosed in U.S. Pat. No. 5,719,584 to Otto, assigned to Harris Corporation of Melbourne, Fla., the disclosure which is hereby incorporated by reference in its entirety. This signal could be a conventional wireless phone signal. One drawback of a non-GPS based system is the expensive infrastructure of associated receiver sites that typically are required in order to measure the desired characteristics of the signal transmitted by a mobile unit. Additionally, receiver sites having these types of receivers often must be spaced relatively close together because the signal transmitted by the mobile unit must be received simultaneously at two or more receivers in systems performing a multilateration function.
It is therefore an object of the present invention to provide a system and method of determining the location of a transmitting mobile unit that overcomes the inherent limitations of both GPS and non-GPS based systems to allow the tracking or location of a mobile unit in areas having good GPS reception and in areas having poor GPS reception while minimizing the required infrastructure.
In accordance with the present invention, a system determines the location of a transmitting mobile unit and includes a mobile unit having a global positioning system (GPS) unit and a transmitter for transmitting an RF communication signal comprising an identification of the mobile unit and GPS data, such as latitude and longitude information or other data obtained from the GPS signal, if available. At least one receiver is contained within an area having good GPS reception for receiving a transmitted signal from the mobile unit when in the area relating to the identification of the mobile unit and the GPS location coordinates or other measured data obtained from the GPS unit. Typically, there would be a plurality of the receivers in this area having good GPS reception to form a first network infrastructure. At least one additional receiver forming a second network infrastructure is contained within an area having poor GPS reception, such as an urban area, for receiving transmitted signals from the mobile unit relating to an identification of the mobile unit and for measuring the angle of arrival and/or the time of arrival, multipath profile, or other characteristics of transmitted signals from the mobile unit. These measured parameters are used for determining the location of the mobile unit. Typically, there would be a plurality of the receivers in this area having poor GPS reception.
In one aspect of the present invention, a processor is operatively connected to the second receiver or plurality of receivers forming the second infrastructure for computing the location of a mobile unit based on the measured angle of arrival and/or time of arrival, multipath profile, or other characteristics. A network processor is operatively connected to the first and second plurality of receivers forming the first and second infrastructures for maintaining a real time record of the location of the mobile unit as it travels throughout the areas having good GPS reception and areas having poor GPS reception. A report generator can be connected to the network processor to generate a report of the location of the mobile unit, which could be necessary in some instances where tracking is required, as in convict location determination.
Typically, the mobile unit can comprise a wireless phone or could comprise a small transmitter employing other RF communication means that could be placed on a body for personal tracking of people, such as convicts or small children. Also, the transmitted signal could comprise an emergency transmit signal to a 911 call center.
In still another aspect of the present invention, the system for determining the location of a transmitting mobile unit comprises a mobile unit having a global positioning system (GPS) unit and a spread spectrum transmitter for transmitting a wideband signal, such as a chirp, containing modulated digital data that includes an identification of the mobile unit and GPS location coordinates, if available. At least one receiver is contained within an area having good GPS reception for receiving a transmitted signal from the mobile unit relating to an identification of the mobile unit and GPS data coordinates obtained from the GPS unit when the mobile unit is located in the area.
At least one second receiver forms a second infrastructure and is contained within an area having poor GPS reception, such as an urban area, for receiving transmitted signals from a mobile unit relating to an identification of the mobile unit and for measuring the angle of arrival of a signal and/or the time of arrival of transmitted signals from the mobile unit to determine the location of the mobile unit. Each of the receivers can comprise a chirp signal generator and a mixer which periodically mixes a lower frequency signal with the chirp signal received from the chirp signal generator to produce a wave signal having a frequency related to a time relationship between the start of the chirp signal and the start of digital data. This type of apparatus is advantageous for use in small pocket transmitters and is sufficient for a large number of users in an area.
In still another aspect of the present invention, the system for determining the location of a mobile device can comprise a mobile unit having a global positioning system (GPS) receiver and a cellular transceiver unit is used for transmitting an RF communication signal comprising a transmitted message, an identification, and GPS location coordinates or other data, if available. A first plurality of cellular base stations forms a first infrastructure and are contained within an area having good GPS reception for receiving a transmitted signal from the mobile unit. The signal comprises a message portion and a portion relating to an identification for the mobile unit and GPS location coordinates or other data obtained from the GPS unit.
At least one second cellular base station forms a second infrastructure and can be contained within areas having poor GPS reception for receiving a transmitted signal from the mobile unit where the signal includes a message and an identification of the mobile unit. Each cellular base station in the second infrastructure has an overlay network receiver for receiving a transmitted signal from the cellular phone and measuring the angle of arrival, and/or the time of arrival, multipath profile or other characteristics of the transmitted signals from the mobile unit. A processor is operatively connected to the second infrastructure of cellular base stations and overlay receivers for computing the location of the mobile unit contained within the area covered by the second receiver or receivers based on the measured angle of arrival and/or time of arrival, multipath profile or other characteristics.
In a method aspect of the present invention, the method obtains data from a GPS unit and may be used to determine determines the location of a transmitting mobile unit and comprises the step of transmitting an RF signal comprising an identification and GPS location coordinates or other data, if available, from a mobile unit that comprises a global positioning system (GPS) unit and transmitter. The method also includes the step of receiving a transmitted signal within an area having poor GPS reception from the mobile unit relating to an identification of the mobile unit within at least one receiver contained within an area having poor GPS reception. The method further comprises the step of measuring the angle of arrival and/or the time of arrival, multipath profile or other characteristics of transmitted signals from the mobile unit to determine the location of the mobile unit.